A human diver in a cold water environment is subject to a considerable heat loss or drain. So great is this heat drain that, in the absence of adequate thermal protection, i.e., insulation, his body becomes hypothermic. This means that the body temperatures decrease, not only externally or peripherally, but also internally, as manifested in the inner core temperature. A human's body core temperature must be maintained at about 37.degree. C. for comfort and safety.
Water temperatures in most parts of the world are normally substantially less than this required human body core temperature. Indeed, water temperatures in the oceans, lakes and rivers of the temperature zones of the world are frequently in the range from about 0.degree. C. to said +15.degree. C. Water has a high specific heat and thermal conductivity compared to air, the normal environment for humans. A human body in water, therefore, will be subject to considerable convective thermal stress due to heat loss driven by the temperature differential between the body and the surrounding water.
Thus, whether a human being is in water for recreation, by virtue of an accident, or working as in the case of divers, the body is subject to the convective thermal stress mentioned above. Regardless of the circumstances, it is very important to maintain the body's core temperature at about 37.degree. C. A drop of core temperature of 2.degree. C., resulting from a heat loss of about 150 kilocalories, can cause mental deficiencies detremental to the safety of the person. A total body heat loss of about 700 kilocalories with a further drop in the core temperature of 5.degree. C. to about 30.degree. C. usually will result in unconsciousness and heart failure.
The actual time taken to undergo a 2.degree. C. or 7.degree. C. drop in body core temperature will vary. The variation can be from only several minutes to up to about an hour, for an unprotected body in extremely cold water. In any event, the human body is incapable of defending itself against the rate of heat loss in such water.
Thus it is essential to provide for a diver or other person in cold water adequate thermal protection during the time such a person is undergoing substantial convective heat loss.